"The really good news here is that it's about polish, grooming, and being put together," Hewlett says. "It's not about the precise shape of your body, texture of your hair, or the designer you wear."

As part of researching her book, Hewlett and her team at the Center for Talent Innovation did a survey of 4,000 professionals in the U.S., including 268 senior executives, hoping to decode what businesspeople think "capable" looks and sounds like.

The senior execs say that the following five qualities of appearance make people instantly look like leaders:

1. Looking polished and groomed.

"Carelessness seems to signal that you don't respect your coworkers or yourself," Hewlett says, "and you certainly don't respect the client if you show up with soup on your tie or bitten nails, anything to make you look unkempt."

To avoid that, clean up. If you're working in Silicon Valley, make sure you've got the appropriate skinny jeans; if you're on Wall Street, snag the perfectly cut jacket. And remember to brush your hair.

"Being physically fit gives people the confidence that you will take care of what you are asked to do, because you are taking care of yourself," GE executive Deb Elam tells Hewlett.

3. Dressing in simple, stylish clothes.

"Dress for your next job," Hewlett says.

To know how to do that, observe the people in your organization who dress well, then pattern yourself after them.

"It's not that everyone has to wear a gray suit," she says, "but this sense of polish and putting some thought into it does yield some benefits."

4. Stand tall.

The importance of height is seriously gendered. According to Hewlett's research, 6% of respondents said that being tall contributed to a woman's executive presence, while 16% said it mattered for a man's.

Looking youthful, but not like a child, signals that you have the "vitality to lead the charge and not succumb to setback," Hewlett writes. She sees the need evidenced in the cosmetic surgery market, as the number of Botox injections, facelifts, and "upper arm lift" operations continue to increase year over year.

But no matter how you're presenting yourself, you need to be aware of the audience you're about to impress.

"If you're headquartered in New York and making a presentation in Mountain View, do some adjusting to how you show up," she says, such as opting for a more California casual look.